1. Field of the Invention.
The present invention relates generally to devices for perforating sheets for insertion in loose-leaf ring binders and, more particularly, to an improved paper punch adapted to be carried in a loose-leaf ring binder.
2. The Prior Art
Devices for perforating sheets for insertion in loose-leaf ring binders and adapted to be carried therein have been around for a long time. Faifer disclosed such a combined perforator and binder in 1915, see his U.S. Pat. No. 1,142,032. Improvements followed. See U.S. Pat. Nos. 1,567,643, granted to Hearne in 1925; 2,139,159, granted to Hammen in 1938; 2,370,319, granted to Lippincott in 1945; 2,495,687, granted to Belmont in 1950; and 3,172,325, granted to Wernham et al. in 1965, to name a few.
In said copending application Ser. No. 08/061,427, filed May 6, 1993, and assigned to a common assignee, Clix Products Inc., of Natick, Mass., there is disclosed a sheet perforating punch, including a pair of punch and die plates rotatably hinged to one another about a pivot point located centrally between the plates. The punch is formed of hard polymeric material. The present invention represents an improvement thereover.
As known and as exemplified by the patents referred to above, it is advantageous to have a perforating device which is designed to be carried in a loose-leaf ring binder so that papers intended to be inserted therein can be punched immediately prior to insertion.
Most, if not all, perforating devices excepting the one disclosed in said copending application, were formed of metal for accurate long lasting punching use. As stated in said copending application, "A major problem arising out of the use of comparatively inexpensive, high molecular weight polymers (hereinafter plastics) for the working parts of paper punches is that unless strict registration is maintained between the punch teeth, they wear very rapidly by engagement with the edges of the die holes or fail to effect the desired punching. The problem is exacerbated when using plastic materials that tend to be less rigid than metals and otherwise more readily deformable and less resistant to wear. Further, many paper punches formed of plastic are easily disassembled, and after several separations and reconnections, both the rotation of the hinges and the registration of holes and teeth are degraded seriously, rendering the punch relatively ineffective."
The above problems have been addressed by the invention disclosed in said copending application, with varying degrees of success. There is still room left for improvements.